Transporting semen (germplasm), e.g., equine or canine semen, is beneficial to breeders for several reasons. Shipping semen is less costly than transporting female horses or dogs to an unfamiliar facility. Stress and risk of disease are minimized when female horses or dogs can remain at home. Further, using artificial insemination allows a stallion to service more mares than he could using natural service, and allows the stallion to continue to show or perform during the breeding season. When shipped semen is handled properly, pregnancy rates approach those achieved using natural service. Semen destined for transport is collected from a male, examined and cooled for shipment. The development of conventional systems allowing controlled cooling has been instrumental. The advantages of using cooled semen make it a valuable addition to breeding programs and has been used to increase the genetic pool in many breeds.
However, numerous factors influence pregnancy rates achieved when mares are bred with transported, cooled stallion semen. For instance, sperm are very sensitive to many environmental factors, including temperature, light, physical trauma, and a variety of chemicals. Any factor that impacts the ability of sperm to resist environmentally-induced damage will adversely affect fertility achieved when using cooled transported semen. Semen must be handled from collection to insemination in such a manner as to not shock nor damage the sperm. If collection or storage devices are contaminated by bacteria, chemicals, or even soap residue, the survivability of the sperm cells can be severely diminished. Proper temperature control of semen prior to cooling and prior to insemination is crucial. For example, if semen is initially mixed with extender that is too cool or too warm, damage will likely occur.
Mares will ovulate 24 to 48 hours before the end of heat and pregnancy rates from cooled stallion semen are the highest when mares are inseminated within 24 hours following semen collection. Some stallion semen is still highly viable up to 48 hours following collection. Semen transported and stored for up to 72 hours may appear to have good motility, but fertilization capabilities are typically poor. Thus, when it is required to transport equine semen samples over long distances or even overseas, it is typically necessary to maintain the motility and fertility of the spermatozoa for 48 hours, at the very minimum, and ideally for more than 72 hours, in order that samples reach its destination and can be effectively used. However, until the development of the present invention, it has been virtually impossible, when using conventional postal/courier services, to achieve this. More specifically, although semen specimens can be transported for such prolonged periods of time if special motorized refrigeration units are used, the costs of such apparatus and the weight penalties incurred when air mail/freight is involved, are prohibitive. Thus, there has been a long felt need for an inexpensive and disposable container that is self-contained (viz., passively cooled) and sufficiently light to enable ready dispatch by conventional delivery/mail services.
One example of a passively cooled, self-contained transportation container, that has been proposed to transport equine semen is disclosed in U.S. Pat. No. 4,530,816 issued to Douglas-Hamilton on Jul. 23, 1985. In this arrangement, which has been marketed under the name Equitainer.TM., the specimen is enclosed in a plastic bag and placed in a metal cup in a manner wherein it is sandwiched between bags of liquid, such as water, that act as so called thermal ballast. The lower portion of the container is filled with a refrigerant can filled with ice or gelatinized ice. A thermal insulating layer, made of a vulcanized rubber, is disposed between the refrigerant (ice) and the metal cup (made of copper sheet 1/32" thick, for example) in which the sample and the thermal ballast bags are disposed. The '816 patent discloses that the optimum steady state temperature is close to, but slightly greater than, 0.degree. C., and in a temperature range of from 4.degree. C. to 10.degree. C. When the semen specimen, which is enclosed in a plastic bag, is placed in the metal cup, it is allowed to cool at a rate of 0.3.degree. C./min until the temperature of the specimen reaches about 5.degree. C., it may be stored for about 30 hours.
Spermatozoa from most animal species are susceptible to irreversible damage if exposed to a sudden drop in temperature, also known as "cold shock." It is known that stallion spermatozoa are more susceptible to cold shock than bovine, ovine, or porcine spermatozoa. Cold shock is generally considered to be the result of rapid cooling from 20.degree. C. to 8.degree. C. It is known that semen can be cooled relatively quickly from about 37.degree. C. (99.degree. F.) down to about 20.degree. C., but must be slow cooled at a rate of 0.05.degree. C./min from 20.degree. C. to 5.degree. C. (47.degree. F.). The above described and other shipping containers have been developed which purport to cool stallion semen at a correct, prescribed rate. Generally, these conventionally available containers generally cool semen over a 10 hour period, and hold the semen at 50.degree. C. (47.degree. F.). It is suspected that the cooling rate achieved by these devices is, in at least a certain temperature range, too rapid, and undesirable "cold shock" frequently occurs to a portion of a semen specimen. During the development of the present invention, however, it was discovered that, after the temperature of collected semen has fallen to about 15.degree. C., the sensitivity of the semen to cold shock is heightened. In overlooking this fact, it is believed that conventionally available containers undesirably reduce the viability of semen samples transported/stored therein.
Of the factors believed to influence the length of time over which viable semen specimens can be successfully transported, water is particularly toxic and exposure to even small amounts of moisture is highly injurious to semen. The fact that the preferred refrigerant disclosed in the '816 patent is ice or a mixture of ice and gelatin water, is also suspected to have an adverse effect on the longevity of a semen sample transported therein, particularly after the ice melts and assumes a fluid liquid form. A drawback with this prior art arrangement is that it tends to promote the accumulation of substantial amounts of condensation, such as water, which not only aggravates the problems associated with the spilt/extended semen (causing objectionable odors, and providing an environment in which various types of microorganisms may spawn and render it very difficult to maintain aseptic conditions), but, as mentioned above, also effectively functions as a powerful spermicide. Accordingly, during transport this condensate can seep into the container in which the semen is stored, and present a serious risk of catastrophic damage to the semen sample. It is also noted that plastic thermal ballast bags of the kind disclosed in the container of the '816 patent are filled with a colored liquid that has a high thermal inertia (high heat capacity) as does water. Leakage of these containers, which may occur during a rough transit, and/or poor storage/handling by the end user prior to disposition in the container, also presents the same problem because condensate tends to accumulate.
One attempt to improve upon the arrangement disclosed in the '816 patent took the form of a foamed plastic container that was marketed under the name Equine Express.TM.. This arrangement provided a simple plug-like door and a commercially available bottle type of refrigerant pack that was placed in the container on top of a thermal insulating layer that was interposed between the refrigerant pack and the samples. However, this arrangement proved to be unable to cool and maintain the sample in the required condition for more than about 45 hours, as is shown in test results reported herein.
Accordingly, there remains a need for a container that allows for transporting samples of equine semen over long distances while at the same time maintaining the motility and fertility of the transported spermatozoa for at least 48 hours without the attendant disadvantages of conventionally available containers and methods.